1. Field of the Invention
The present invention relates in general to a method of detecting color deviation in a color image forming apparatus such as a color printer and a color copying machine, and an image-formation article such as a test sheet, which is used in detecting the color deviation and which comprises color-deviation-detecting images formed thereon. The invention also relates to a control device which controls the color image forming apparatus such that the apparatus is capable of executing operations relating to the detection of the color deviation, and a control program for controlling the color image forming apparatus to execute the operations.
2. Discussion of Related Art
In general, a color image forming apparatus such as a color printer and a color copying machine forms a color image by superposing a plurality of monocolor images on one another. Described in detail, for instance, the color image forming apparatus is equipped with image forming units respectively for coloring materials having the respective plurality of colors. The image forming units are moved relative to a base object such as a printing sheet, for instance, which is an image-formation medium, and the coloring materials are attached to the surface of the base object at respective appropriate positions thereof, so that the color image is formed. A phenomenon that the positions of the monocolor images provided by the respective plurality of colors and formed by the respective image forming units deviate from one another, in other words, color deviation or out of color registration deteriorates the quality of the color image to be formed by the color image forming apparatus. It is important to properly or suitably detect the color deviation for maintaining or improving the quality of the color image. Further, it is possible to obtain a high-quality color image by inhibiting the color deviation. In view of the above, JP-A-2001-7949 discloses a method of detecting color deviation in the color image.
The detecting method disclosed in JP-A-2001-7949 is arranged to detect an amount of deviation of positions of two monocolor images based on a color of an image in which the two monocolor images respectively having predetermined patterns are superposed on each other. Since, in the disclosed method, the positional deviation amount is not directly measured, the disclosed method permits easy detection of the color deviation. However, there may occur a phenomenon that the monocolor images are not formed so as to have the respective predetermined patterns, due to aged deterioration of the color image forming apparatus, the environment in which the apparatus is disposed, etc. Further, there may occur a phenomenon that the colors of the superposed image change due to the influence of the color of the image-formation medium, the influence of the coloring materials to be attached or the amounts thereof to be attached, etc. Such phenomena are factors that deteriorate an accuracy of detection of the color deviation. Thus, in the light of an increasing demand for improvement in the quality of the color image, the disclosed method is not practical to a satisfactory extent.